AIC1570 Datasheet, PDF (15/18 Pages) Analog Intergrations Corporation – 5-bit DAC, Synchronous PWM Power Regulator with LDO and Linear Controller

AIC1570
case capacitor.
Output Inductor Selection
Inductor value and type should be chosen based
on output slew rate requirement, output ripple
requirement and expected peak current. Inductor
value is primarily controlled by the required
current response time. The AIC1570 will provide
either 0% or 100% duty cycle in response to a
load transient. The response time to a transient is
different for the application of load and remove of
load.
tRISE
=
L × ∆IOUT
VIN − VOUT
,
tFALL
=
L
× ∆IOUT
VOUT
.
Where ∆IOUT is transient
load current step.
In a typical 5V input, 2V output application, a 3µH
inductor has a 1A/µS rise time, resulting in a 5µS
delay in responding to a 5A load current step. To
optimize performance, different combinations of
input and output voltage and expected loads may
require different inductor value. A smaller value of
inductor will improve the transient response at
the expense of increase output ripple voltage and
inductor core saturation rating.
Peak current in the inductor will be equal to the
maximum output load current plus half of inductor
ripple current. The ripple current is approximately
equal to:
IRIPPLE
=
(VIN
− VOUT) × VOUT
f × L × VIN
;
f = AIC1570 oscillator frequency.
The inductor must be able to withstand peak
current without saturation, and the copper
resistance in the winding should be kept as low
as possible to minimize resistive power loss
Input Capacitor Selection
Most of the input supply current is supplied by the
input bypass capacitor, the resulting RMS current
flow in the input capacitor will heat it up. Use a
mix of input bulk capacitors to control the voltage
overshoot across the upper MOSFET. The
ceramic capacitance for the high frequency
decoupling should be placed very close to the
upper MOSFET to suppress the voltage induced
in the parasitic circuit impedance. The buck
capacitors to supply the RMS current is
approximate equal to:
IRMS = (1− D) ×
D×
I²
OUT
+
1
12
×
ç
VIN × D
f ×L
÷
2
, where
D
=
VOUT
VIN
The capacitor voltage rating should be at least
1.25 times greater than the maximum input
voltage.
PWM MOSFET Selection
In high current PWM application, the MOSFET
power dissipation, package type and heatsink are
the dominant design factors. The conduction loss
is the only component of power dissipation for the
lower MOSFET, since it turns on into near zero
voltage. The upper MOSFET has conduction loss
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